[dotnet-port-fixes] Align skills prompt placeholders with .NET

[michelle-clayton-work]

Port upstream .NET behavior from microsoft/agent-framework#6706 so custom skills prompt templates only require the {skills} placeholder. Legacy resource and script instruction placeholders are no longer specially substituted; default guidance remains embedded in the default prompt.

• [dotnet-port-fixes] Align skills prompt placeholders with .NET #372

[Copilot]

Pull request overview

Aligns the Go agent/skills context provider’s prompt-template placeholder behavior with the upstream .NET implementation by making {skills} the only required placeholder in custom templates and embedding resource/script guidance directly in the default prompt.

Changes:

• Remove special substitution and validation for legacy {resource_instructions} / {script_instructions} placeholders; only {skills} is required and substituted.
• Embed resource/script usage guidance in the default skills instruction prompt instead of injecting it via placeholders.
• Update tests to validate the new behavior (custom templates don’t receive default guidance; legacy placeholders remain literal if present).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
agent/skills/provider.go	Simplifies placeholder handling to only {skills}, embeds default resource/script guidance, and updates template validation accordingly.
agent/skills/provider_test.go	Updates/extends unit tests to cover acceptance of missing legacy placeholders and literal retention of legacy tokens.
agent/skills/skills_test.go	Adjusts the custom prompt template test to only use {skills}.

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[github-actions]

Generated by Go API Consistency Review Agent for #392 · 190.5 AIC · ⌖ 12.8 AIC · ⊞ 28.8K

[github-actions]

Cross-SDK parity review

This PR faithfully ports the .NET behavior from microsoft/agent-framework#6706. The Go implementation now aligns with .NET on the following points:

• Custom SkillsInstructionPrompt templates only require {skills} ✅
• Resource and script-tool guidance is embedded as literal text in the default template ✅
• validatePromptTemplate checks only for {skills} ✅
• Legacy {resource_instructions} / {script_instructions} tokens in custom templates render literally (not substituted) ✅

Parity gap to track — Python vs. Go/.NET on custom-template injection

The upstream Python implementation (python/packages/core/agent_framework/_skills.py) behaves slightly differently for custom templates:

# Python: _build_instructions calls str.format() with all three substitutions,
# so a custom template CAN reference these optional placeholders:
return template.format(
    skills="\n".join(lines),
    runner_instructions=runner_instructions or "",   # SCRIPT_RUNNER_INSTRUCTIONS constant
    resource_instructions=resource_instructions or "",  # RESOURCE_INSTRUCTIONS constant
)

Python's default template is:

{skills}
...
{resource_instructions}
{runner_instructions}

This means:

1. A Python custom template that contains {resource_instructions} or {runner_instructions} will have those tokens filled with the standard guidance constants (not remain literal).
2. In Go (and .NET), the equivalent tokens {resource_instructions} / {script_instructions} render literally in custom templates — they are not substituted.

Additionally, Python's active placeholder for script instructions is {runner_instructions}, while Go historically used {script_instructions}. The renaming to "legacy" in Go tests is correct for Go, but these are different names than the Python constant.

Impact: Low for most users (default template is unchanged). Users migrating custom templates across SDKs, or adopting the Python convention of referencing {resource_instructions} in a custom template, will get different runtime behavior in Go vs. Python. The gap is worth tracking as a follow-up item against the Python implementation, but is not a blocker for this .NET-tracking port.

Summary: No issues blocking this PR. The Go change correctly mirrors the merged .NET behavior. The Python parity gap on optional custom-template injection predates this PR and should be tracked separately against the Python SDK.

Generated by Go API Consistency Review Agent for #392 · 227.7 AIC · ⌖ 12.6 AIC · ⊞ 27.1K · ◷